2.5维海洋非线性共轭梯度反演应用效果研究

为了研究频率域2.5维非线性共轭梯度反演在海洋天然气水合物探测中的实际应用效果,利用美国Scripps研究所在South Hydrate海域采集的可控源电磁探测数据进行2.5维非线性共轭梯度反演计算,结合其他地球物理方法在同一海区的研究结果,综合分析2.5维反演计算的准确性和有效性。结果表明,非线性共轭梯度反演能够清晰地反映出该区域海底面以下1~2 km地层的电导率结构分布,其局部反演结果与地震反射、地震层序、测井分析结果基本一致,且对小尺寸异常、浅层高阻体分辨力较强,尤其在海洋天然气水合物探测方面具有较大潜力。

Study on the Application Effect of 2.5 D Marine Inversion Using the Nonlinear Conjugate Gradient Algorithm

This paper aims to research the application effect of 2.5-dimension nonlinear conjugate gradient inversion in frequency domain in the field of natural gas hydrate detection. The effectiveness of self developed 2.5 dimensional nonlinear conjugate gradient inversion algorithm has been tested through the data obtained from the South Hydrate sea area, Oregon, the United States. These data was collected through controlled source electromagnetic detection by the Scripps Institution of Oceanography in 2004. Beneath the seafloor of this area, free gas and gas hydrate have been proved to exist. Many different kinds of geophysical exploration methods have been applied within this zone. The inversion results of nonlinear conjugate gradient algorithm clearly illustrate the electrical conductivity distribution of the area 1-2 km under seafloor. The results have a remarkable meaning in the comparison research of the OCCAM inversion result for the same region. Furthermore, the details of nonlinear conjugate gradient inversion conform to the conclusions of marine magnetotelluric method, seismic reflection method, seismic sequence stratigraphy and ocean drilling programs. Therefore, the 2.5-dimension nonlinear conjugate gradient algorithm is capable of reflecting the conductivity distribution of shallow seafloor rather deliberately and exactly. This inversion method shows great potential in application, especially for small-scale reservoir, shallow buried resistivity and marine gas hydrate.